Method and a device for purifying water

ABSTRACT

The invention relates to a method and a device for purifying water used for forming a water curtain of a wet spray wall in paint spray and/or glue processing booths, wet dust removal plants and the like. The water to be purified is caught in a receptacle (1) and the water is sucked out under the surface of the water present in said receptacle (1), mixed with air and introduced into a basin (14) at the bottom side of said basin (14). The water mixed with air is introduced into a basin (14) which widens in upward direction, and contaminations floating on the surface of the water present in said basin (14) are pushed towards an outlet disposed near one side of said basin (14) by means of a pusher, whilst the water flows out on the opposite side of the basin via an overflow. A few perforated plates disposed one above the other are provided in the basin (14) whose sectional area gradually increases in upward direction.

The invention relates to a method for purifying water, for example waterused for forming a water curtain of a wet spray wall in paint sprayand/or glue processing booths, wet dust removal plants and the like,whereby the water to be purified is caught in a receptacle and the wateris sucked out under the surface of the water present in said receptacle,mixed with air and introduced into a basin at the bottom side of saidbasin, wherein the water mixed with air is introduced into a basin whichwidens in upward direction, and that contaminations floating on thesurface of the water present in said basin is pushed towards an outletdisposed near one side of said basin by means of a pusher, whilst thewater flows out on the opposite side of the basin via an overflow, whichis screened at its side facing the outlet for the contaminations by apartition extending slightly below the water level in the basin.

From DE-U-9313340 there could be derived such a method wherein the wateris passed through a basin comprising a lower conical part, a cylindricalmiddle part and a widening upper part whereby in the bath there have notbeen provided means obstructing the upward flow of the water.

U.S. Pat No. 4,610,785 discloses a method and a device of this kind,wherein the water is injected through a pipe in the longitudinaldirection of a trough-shaped bottom end of the basin, in such a mannerthat the water collides with a partition disposed in the basin at somedistance from the end of said pipe, as a result of which the water isimparted a turbulent motion about an imaginary axis extendinghorizontally and perpendicularly to the longitudinal direction of saidpipe. The discharge of the water takes place through a discharge channellocated on one side of the basin, which is separated from the other partof the basin by a partition, the bottom edge of said partition beinglocated a short distance above the supply pipe.

In practise it has become apparant the primarily heavier particles, theslightly larger, more crystalline particles, will thereby float on thewater surface, whilst the lighter particles, the smaller, more colloidalparticles, are carried towards the outlet by the water as a result ofthe strong turbulent flow of the water, so that an adequate purificationof the water casu quo separation of particles is not obtained.

From EP-A-0,065,382 a method and a device for purifying water can bederived wherein part of the contaminated water is introduced in a basinnear the upper side of said basin and another part of the water isintroduced into said basin near the bottom side thereof. Thecontaminations floating on the water surface are thereby swept out ofthe basin near one side thereof, whilst a discharge pipe for thedischarge of water from the basin is connected to the basin near thesame side thereof. Also here the introduction of contaminated water intwo places causes a strong turbulence of the water in the basin, as aresult of which an adequate separation in particular of light particlesfrom the water can not be effected. Furthermore the aimed-at separationbetween liquid and particles is made more difficult because thedischarge of water from the basin and the discharge of particlesfloating on the water take place in places located in close proximity toeach other.

The method according the invention is characterised in that in thelowermost part of the basin which widens up along the entire length ofits height the water is passed through perforated plates being disposedone above the other and after passing said screens the water is passedinto an upper part of the basin where the increase of the cross-sectionmeasured in a horizontal direction per unit of height is greater as inthe lowermost part of the basin.

When using a method according to the invention a very gradual rising ofthe air divided into fine air bubbles in the liquid is obtained, as aresult of which contaminations are effectively driven towards thesurface, whereby, as has become apparent in practice, alsocontaminations in the form of paint traces and/or other types ofcontamination will float on the water surface and be discharged on oneside of the device. Since there is no generation of a strong turbulencenear the partition disposed before the overflow, which partition extendsonly slightly below the level of the water present in the basin, therisk of contamination in particles being swept along by the waterflowing out is largely avoided.

Another aspect of the invention relates to a device for purifying water,for example water used for forming a water screen in a paint sprayand/or glue processing booth, whereby said device is provided with areceptacle for the water, in which at least one suction means isdisposed, which is connected to the suction side of a pump, whilst aventuri is provided between the pump and the suction means for mixingthe intake water with air and the delivery side of the pump is connectedto the bottom side of a basin, said basin on one side, near the upperside, being provided with an outlet for the discharge of contaminationsfloating on the water present in the basin, whilst an overflow for thedischarge of water from the basin is disposed near the side remote fromsaid outlet and the overflow is separated from the remaining part of thebasin by a partition extending slightly below the water level duringnormal operation. According to the invention a few perforated platesbeing disposed one above the other are thereby provided in the basin,whose sectional area gradually increases in upward direction.

By using a device of this type a very uniform movement and distributionof the air bubbles rising towards the surface in the basin is obtainedas a result of the gradually increasing, in upward direction, sectionalarea of the basin in conjunction with the perforated plates, as a resultof which contaminations present in the liquid are effectively caused torise to the surface, so that said contaminations will float on the watersurface and be discharged from there, whilst the outflow of the purifiedwater will not cause any undesirable turbulence in the liquid present inthe basin.

The invention will be explained in more detail hereafter with referenceto an embodiment of the device according to the inventiondiagrammatically illustrated in the accompanying figures.

FIG. 1 is a diagrammatic representation of the device according to theinvention.

FIG. 2 is a plan view of one embodiment of a suction funnel.

FIG. 3 is a side view of FIG. 2.

FIG. 4 is a plan view of another possible embodiment of a suctionfunnel, only half of which is shown in this figure.

FIG. 5 is a side view of FIG. 4.

FIG. 6 is a larger-scale, diagrammatic view of the basin of the deviceaccording to the invention.

FIG. 7 is a diagrammatic view of a strickling mechanism.

FIG. 8 is a larger-scale view of a part of a scraper of the stricklingmechanism.

FIG. 9 is a sectional view of a venturi to be used in the deviceaccording to the invention.

FIG. 1 diagrammatically indicates a wall 1, for example a wall of aspray booth, along which a water screen consisting of water flowing fromthe upper side of said wall to the bottom side thereof is formed, in amanner known per se, during operation.

Said water is caught in a receptacle 2 disposed near the bottom side ofthe screen, wherein the water level will be as indicated by dotted line3 during normal operation.

In the illustrated embodiment two suction funnels 4 and 5 are disposedin receptacle 2, to which suction stubs 6 and 7 respectively areconnected.

As is shown in FIGS. 2 and 3, such a suction funnel may consist of acircular, dish-shaped means 8, to the bottom of which a suction stub maybe connected.

As is shown in FIGS. 4 and 5, such a suction funnel may also consist ofan elongated rectangular trough 9, however, whereby the suction stubwill also be connected to the lowest point of the bottom of said trough.Thus various forms and dimensions of the suction funnel will bepossible, inter alia depending on the shape of the receptacle and/or therequired capacity of the suction funnel.

Said suction funnels 4 and 5 are connected, via suction stubs 6 and 7,to a line 10, which is in communication with the suction side of a pump12 via a venturi 11. The size, arrangement and dimensions of saidventuri depend on the purpose for which the venturi is used. Connectedto the delivery side of the pump is a line 13, which connects the pump12, possibly via provisions for the injection and mixing of chemicalswhich may have a positive effect on the process, to a stub 15 (FIG. 6)connected to the bottom end of a basin 14, in which stub a non-returnvalve (not shown) is incorporated in order to prevent water from flowingback out of the basin.

As will be apparent in particular from FIG. 6, the sectional area of thebasin gradually increases from the bottom to the top, whilst thesectional area of the basin increases strongly, in particular near theupper side of the basin, as a result of the presence of a wall part 16of the basin, which extends to the left, seen in FIG. 6, and whichincludes a comparatively small angle (less than 30°) with thehorizontal. Connected to the left-hand end of said wall 16 part is anoutlet line 17, which opens above a filtering device 18 (FIG. 1).

A filtering bag (not shown) is disposed within said filtering device 18,in which filtering bag contaminations discharged along with water viadischarge line 17 are caught. Filtering unit 18 is furthermore connectedto venturi 11 via a line 19, which is fitted with a cock 20.

A discharge bin 21 is disposed near the right-hand upper side of thebasin, seen in FIG. 6, to which discharge bin a discharge stub 22 isconnected (FIG. 6).

The discharge bin 21 is bounded by a vertically adjustable partition 23forming an overflow, by means of which the water level in basin 14 canbe determined.

A partition 24 extending parallel to partition 23 is fixedly disposed inthe basin, said partition 24 being spaced from partition 23 by a shortdistance. During normal operation the bottom side of said partition willextend under the water surface and thereby prevent contaminationsfloating on the water from flowing into the discharge bin 21 via channel25, which is bounded by the two partitions 23 and 24.

A strickling mechanism to be described hereafter with reference to FIGS.7 and 8 is disposed near the upper side of the basin, said stricklingmechanism comprising a scraper or pusher means, which will pushcontaminations floating on the water present in the basin in thedirection of the discharge line or outlet 17 during its movement in thedirection of discharge line 17, whilst the scraper will have been movedto a position above the water level during its return movement towardsthe discharge channel 25.

The discharge stub 22 is in turn connected to receptacle 2 via one ormore return lines 26.

As is furthermore apparent from FIG. 6, perforated plates 27-29comprising passages having a diameter of 20, 15 and 10 mm respectivelymay be provided at different levels in the basin 14, depending on theintended use and the capacity.

If desired an agent may be added to the water to prevent thecontamination particles, for example paint particles if used with aspray booth, from bonding strongly together, as a result of whichaddition the contaminative particles will be more inclined to remainafloat on the surface of the water in receptacle 2.

The contaminated upper layer may now be sucked from receptacle 2 via thedischarge funnels 4 and 5, by operating pump 12. Pump 12 may thereby bedisposed at a higher level than discharge funnels 4 and 5, so that thewater from the discharge funnels cannot flow to pump 12 under theinfluence of gravity, or the capacity of pump 12 in proportion to thepassage of lines 6, 7 and 10 may be such that even if pump 12 isdisposed at a lower level than the discharge funnels 4 and 5, thesub-atmospheric pressure being generated is still sufficiently strong tocause the discharge funnels 4 and 5 to be emptied alternately. As aresult of the sub-atmospheric pressure being generated water and airwill first be drawn in at a first discharge funnel, whilst the otherfunnel, if emptied before, will fill up thereby.

This effect can be influenced positively by making the diameter of thepassage of the end of line 7 connected to discharge funnel 5 smaller(for example 15 mm) than that of the passage of the end of line 6connected to the other discharge funnel 4 (for example 22 mm).

As soon as the former funnel has been emptied, the sub-atmosphericpressure at the second funnel will be greater than at the first funnel,as a result of which the second funnel will be emptied, whilst theformer funnel will fill up again in the meantime.

The water drawn in by pump 12 is passed through the venturi (shown inFIG. 9) disposed upstream of said pump, whereby the water moves throughsaid venturi in the direction according to arrow W.

Venturi 11 is built up of a tube 37, which is connected to stubs 39 viaconical connecting pieces 38, so as to be connected to the lines beingin communication with discharge stubs 6 and 7 and pump 12 respectively.

An annular insert piece 40 is provided in tube 37. As is apparent fromFIG. 9, the diameter of the passage in said insert piece graduallybecomes smaller in downstream direction. Radial bores 41 are provided inthe insert piece, near the narrowest part of the passage, said boresconnecting the passage to a circular groove 42 provided in the outercircumference of the insert piece 40. Groove 42 is in communication witha stub 43, through which air can be drawn in during operation. Anadjustable shut-off valve or the like may be provided on stub 43 so asto influence the air flow through stub 43.

Directly downstream of the narrowest part of the insert piece 40, whichis provided with air supply passages 41, the diameter of the passageincreases again to the internal diameter of line 37.

Upstream of the stub 43 a bent connecting pipe 44 is provided in theventuri. One end of the connecting pipe projects outside the venturi andis intended for connection to line 19. Inside the venturi saidconnecting pipe 44 is bent in downstream direction, whereby the free endof the tube is located in the passage of the insert piece 40.

The capacity of pump 12, which is preferably a centrifugal pump with asemi-open or closed impeller, is such that a strong sub-atmosphericpressure can be generated in venturi 11 during operation.

As a result of the strong sub-atmospheric pressure in the venturi bothwater and air will be drawn in and be mixed thoroughly, in such a mannerthat the water will contain a large amount of fine air bubbles. Saidmixing is intensified by the sudden increase of the diameter of thepassage for the liquid behind the narrowest part of the venturi.

The contaminated water drawn in by means of pump 12 and mixed with airis pumped into the bottom side of basin 14 via line 13, preferably insuch a manner that the water is imparted a turbulent motion about animaginary vertical axis. The contaminated water will gradually rise insaid basin. The successive perforated plates 27-29 will thereby causethe water to flow upward in the basin in a gradual, calm manner, wherebythe contaminations are pushed upward by the mixture of water and air andwill float on the water in the basin. As a result of the large taperbounded by wall 16 at the upper side of the basin in the direction ofthe discharge pipe the rising water and contaminations will be inclinedto flow in the direction of the discharge line, as a result of which thecontaminations are slightly pushed in the direction of discharge line 17already, whilst clean water can flow from the basin via dischargechannel 25. As is shown in FIG. 6 a diversion plate 30, which divertsthe rising water in the direction of discharge line 17, may furthermorebe disposed under discharge channel 25 in order to prevent contaminationparticles from moving in the direction of said discharge channel 25.

The contamination particles in the water discharged via line 17 arecaught in a filtering unit provided within the filter housing 18. Thewater passing through said filtering unit will be drawn in by pump 12through line 19 and venturi 11.

A mixing of air and water is effected not only via venturi 11 but alsowhen water is being drawn in via discharge funnels 4 and 5, which has apositive effect on the separation of contamination particles.

The water flowing from basin 14 via discharge chamber 21 is returned toreceptacle 2 via line 26, whereby the water, which is still mixed withair, thus flowing into receptacle 2 will cause some stirring of thewater present in receptacle 2, as a result of which contaminationparticles, which tend to settle in receptacle 2, will be driven upwardto the surface of the receptacle, in order to be discharged from there.

The water may furthermore be drawn in from receptacle 2 by means of apump (not shown), and be used in a usual manner again for forming thewater curtain flowing along wall 1.

The filter may be replaced by a clean filter at regular intervals,whilst the fouled filter may be cleaned and/or be discharged and forexample be incinerated.

As is diagrammatically shown in FIG. 7, the scraping mechanism may beprovided with an adjusting means, for example in the shape of aso-called belt cylinder 31, by means of which a slide 32 can be moved toand fro, as is indicated by means of arrow A. A scraper or pusher means34 is coupled to slide 32 by means of a pivot pin 33 extendinghorizontally parallel to the water surface 3. It will be apparent thatsaid pusher means 34 consisting of an elongated plate-shaped member willextend over at least substantially the entire width of the basin.

As is shown in more detail in FIG. 8, a rubber strip 35 may be securedto the underside of pusher means 34.

Pusher means 34 can be pivoted with respect to said slide by means of asetting cylinder 36 between the position shown in FIG. 7, in which thebottom end of said pusher means, in particular the rubber strip 35,extends below the water surface 3, and a pivoted position, in which saidpusher means will be entirely located some distance above the watersurface 3.

Although the invention has been described above in particular withregard to purifying water used in painting units and the like, it willbe apparent that the method and the device may also be used for treatingliquids contaminated in a different manner. Instead of air it will alsobe possible thereby to draw in a suitable gas, if desired.

Of course further modifications and additions to the above-describeddevice are conceivable.

Thus it is possible to dispose devices intended for filtering out coarsepieces or parts which cannot be caused to rise in the basin in theabove-described manner between receptacle 2 and basin 14.

Another possibility is to dispose suitable equipment for re-treatment ofthe water to be fed back between discharge stub 22 and receptacle 2.Furthermore means for the automatic process control, data logging and/ortelemetry elements may be connected to the device.

I claim:
 1. A method for purifying water, comprising:collecting thewater to be purified in a receptacle; sucking a portion of the water outfrom under a surface of the water present in said receptacle; mixing theportion of the water with air; introducing the mixture into a basin at abottom side of said basin, the basin widening in upward direction andincluding a pusher, such that contaminations floating on the surface ofthe water present in said basin are pushed towards an outlet disposednear one side of said basin by the pusher, whilst the water flows out onan opposite side of the basin via an overflow, the overflow beingscreened at a side facing the outlet from the contaminations by apartition extending slightly below the water level in the basin; andpassing the mixture through a plurality of perforated plates disposed inthe basin one above the other to an upper part of the basin, the upperpart of the basin having a cross-section greater than that of alowermost part of the basin.
 2. A method according to claim 1, whereinsaid sucking the portion of the water from the receptacle is effected insuch a manner that air is sucked in along with the water near the watersurface in the receptacle.
 3. A method according to claim 1 or 2,wherein the water to be supplied to the basin is passed through aventuri having at least one air supply line connected thereto.
 4. Adevice for purifying water comprising:a pump having a suction side and adelivery side; a receptacle for the water having at least one suctionmeans disposed therein and connected to the suction side of the pump; aventuri provided between the pump and the at least one suction means formixing the water with air; a basin having a bottom end connected to thedelivery side of the pump, said basin having on an upper side an outletfor the discharge of contaminations floating on the water present in thebasin and an overflow for the discharge of water from the basin, theoverflow disposed near a side remote from said outlet and separated fromthe remaining part of the basin by a partition extending slightly belowthe water level during normal operation; and a plurality of perforatedplates disposed one above the other in the basin whose sectional areagradually increases in upward direction.
 5. A device according to claim4, wherein each of the perforated plates has a different aperaturediameter, the aperture diameter of a particular plate being larger thanthe aperture diameter of a plate positioned at a higher level.
 6. Adevice according to claim 4 or 5, further comprising a diversion platedisposed a distance below said overflow, said diversion plate divertingan upward flow in the direction of the outlet for the contaminations. 7.A device according to claim 4 or 5, wherein said venturi has a narrowestpassage, which is circumferentially provided with regularly distributedair supply holes, and a line portion having a larger diameter than thenarrowest passage, said line portion located directly downstream of saidnarrowest passage of said venturi.
 8. A device according to claim 4 or5, wherein said basin is bounded near an upper side by a wall partsloping upwards in the direction of the outlet, said wall part includinga small angle with the horizontal.
 9. A device according to claim 4 or5, wherein said overflow is bounded by a vertically adjustable means,which may be used to adjust the water level within said basin.
 10. Adevice according to claim 4 or 5, wherein said receptacle included atleast two suction funnels, and wherein the pump generates asub-atmospheric pressure near said suction funnels to empty the suctionfunnels alternately.
 11. A device according to claim 10, wherein saidsuction funnels are connected to said pump via lines having differentdiameters.
 12. A device according to claim 4 or 5, further comprising afiltering device connected to said outlet for the contaminations, andwherein said pump includes a suction pipe connected to said filteringdevice.
 13. A device according to claim 12, wherein said suction pipe isconnected to the venturi via which said pump draws in water from saidreceptacle.
 14. A device according to claim 4 or 5, further comprising apusher means disposed in said basin, said pusher means capable ofreciprocating movement over said basin in order to push contaminationsfloating on the water in the basin in the direction of said outlet. 15.A device according to claim 14, wherein said pusher means is coupled toa slide being capable of reciprocating movement, with respect to whichsaid pusher means can pivot about a horizontal pivot pin.
 16. A deviceaccording to claims 4 or 5, further comprising means for regulating thethrough-flow of water upstream of said venturi, said regulating meansprovided between said venturi and said receptacle.
 17. A deviceaccording to claims 4 or 5, further comprising means for regulating theamount of air drawn in per time unit by the venturi during operation.18. A device according to claims 4 or 5, further comprising means forintroducing and/or mixing chemical agents having a positive influence onthe treatment of the water, said introducing and/or mixing meansprovided in the supply line to said basin.
 19. A device according toclaim 4 or 5, further comprising a plurality of devices for filteringout coarse pieces and the like, said devices disposed between saidreceptacle and said basin.
 20. A device according to claim 4 or 5,further comprising a suitable equipment for retreatment of the water tobe fed back, said suitable equipment provided between a discharge stubof said basin and said receptacle.
 21. A device according to claim 4 or5, further comprising means for automatic process control, data loggingand/or telemetry elements.